The present invention relates generally to an improved gauge means for determining the dimensional suitability of certain starter motor housings for mounting upon specific individual internal combustion engines. The gauge means of the present invention is designed to determine the distance between the surface of a known plane such as the plane of the starter motor receiving pad on an engine block and a location on the teeth of the ring gear surrounding the engine flywheel, with the "location" being, for example, the working depth of a remote gear such as the engine's ring gear. This ring gear typically has a working relationship with the starter motor mounting pad, since the plane of the mounting pad determines the depth or extent of engagement of the teeth of the pinion gear with the mating teeth of the ring gear. While having application for all engines, including newly-manufactured engines, the gauge means of the present invention has particular application for use in connection with reconditioned and/or rebuilt starter motor housings, and is utilized to determine the suitability of certain reconditioned starter motor housings for use and application on individual internal combustion engines. Because this measuring operation involves a blind determination of meshed gear positions, it has been a persistently difficult task, particularly with fully assembled vehicles.
Starter motors are machines and/or mechanisms for rotating engine components, typically the crankshaft, from dwell to a speed at which the engine will start. Starters for internal combustion engines are typically powered by the storage battery, and may range in power from a few horsepower up to at least about 15 horsepower for large diesel engines. Starter motors are designed to produce high power output for short time intervals without generating substantial quantities of heat. This is accomplished by accelerating the engine components to a start-up speed in a relatively short time interval.
The starter motor typically engages the engine components through its pinion gear, with the pinion being positioned on the starter motor shaft. The engine ring gear is normally engaged by the starter pinion, with the ring gear typically being located on the outer circumference of the flywheel.
Pre-engaged starters are now almost exclusively utilized in the automotive field. These starters utilize a solenoid which drives the pinion into mesh with the ring gear prior to delivery of power or current to the starter motor. In addition to driving the pinion, the solenoid typically closes a pair of contacts, the closure of which commences delivery of current to the starter motor. Appropriately indexed pinion gears are utilized to assure alignment between the teeth of the pinion and the teeth of the ring gear. Overriding and/or unidirectional clutches are typically employed to avoid starter motor problems whenever the pinion remains in mesh after the engine is started. While short intervals of post-mesh engagement are common, long or extended periods of post-engagement mesh can cause substantial damage to an ordinary starter motor.
In the manufacture of engine blocks for internal combustion engines, the primary base reference or datum point is the location of the main bearings. On automotive engines in particular, electric starter motors are almost universally utilized for engine-starting purposes. The mounting point for starter motors is typically a pad milled directly on the engine block along or adjacent the oil pan rail. The precise location of the pad including the location of its plane is determined with reference to the main bearings. Manufacturing techniques are such that differences frequently occur in the reference height between the starter motor mounting pad and the main bearings. Because of the anomalies and imperfections which occasionally occur in the production of engine block castings, the precise location and plane of the starter motor mounting pad may vary from engine-to-engine, while at the same time remaining within certain acceptable manufacturing tolerances. For example, it is common to have a variance in the location of the axis of the crankshaft relative to the oil pan rail starter mount. One of the early operations on an engine block is the boring of the crankshaft centerline along with the boring of the main bearings and boring for the oil pan mounting screws. The starter mount is frequently along a plane which extends parallel to the axis of the crankshaft, with the radial spacing between the plane and the crankshaft axis frequently varying from engine-to-engine.
Over the years, the main variation in engine blocks is the difference in height of the pad with reference to the axis of the crankshaft because factory operations may result in cutting of the main bearing bores deeper into the block whenever the original cut or the machining does not appropriately "clean up" the main bearing bore. This, coupled with the natural cumulative effect of tolerances in starter mounting bolt hole location presents and creates the problem solved by the gauge means of the present invention.
With ordinary wear on the engine, and with the usage that occurs over time, the starter motor mounting pad may become damaged and/or worn, and when this occurs, the mounting surface may be reconditioned and/or freshened in order to appropriately receive and securely mount the housing of a starter motor. However, most frequently, problems do arise when the components do not fall within the original manufacturing tolerances, and the engagement of the teeth of the pinion into the ring gear fails to meet the requirements for proper operation.
In the ordinary use and operation of automobiles, engine starter motors frequently wear out, become damaged, or otherwise become unworkable so that replacement is required. In order to reduce the cost and expense to the motorist, there is considerable business activity in the remanufacturing and/or reconditioning of automotive starter motors. For example, the brushes may require replacement, the armatures may require rewinding, and certain of the bearings or bushings may become worn to such an extent that replacement is required. When starter motors are reconditioned, the surface pad which mates with the engine may sometimes require reconditioning and/or freshening as well. If this operation becomes necessary, additional milling is necessary and the distance between the plane of the mounting surface relative to the axis of the pinion shaft is altered, and care must be exercised in order to assure that the proper positioning of the starter pinion with the mating flywheel ring gear is provided. Whenever the starter motor housing requires excessive machining or milling, it may become necessary to interpose shims between the mounting bases in order to provide proper meshing of the teeth of the starter motor pinion with the teeth of the ring gear.
As an added complication, in a typical automotive starting system, the components must be designed for reliable operation at widely varying temperatures. For example, engine temperatures at starting may typically vary within a range of from -40.degree. F. to 240.degree. F. To further aggravate the situation, on certain occasions, there may even be a mis-match in temperature between the flywheel and the starter pinion. At any rate, a persistent problem exists when close operating tolerances must be maintained for both cold and hot starts. The thermal expansion properties of the materials being utilized tend to add to the problem, thereby requiring careful control of the design and the tolerances. In a typical automotive starting system, tolerances not exceeding .+-.0.010 inches are routine. In presently manufactured automotive engines, the desired distance between the tip of the pinion gear and the root of the ring gear, during engagement, is 0.045 inches .+-.0.015 inches. Thus, this distance must be no less than 0.030 inches and not greater than 0.060 inches.